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Chickens Are Bigger Than Ever Before, Researchers Explain Why

Today’s chicken is a gargantuan beast compared to a chicken from the 1950’s. A recent graphic from Oxford’s Poultry Science journal shows that a modern broiler chicken weighs roughly five times more than a broiler chicken from 1957. The modern chicken weighs roughly 10 pounds while it’s 1957 counterpart weighed just under two pounds.

What spurred the change? Most people will probably say hormones are to blame, but that’s not the case. It’s been illegal to treat poultry with hormones since the 1950’s. The change, according to a recent Poultry Science study, is simply a result of selective breeding.

Researcher Dr. Martin Zuidhof and his team performed the study in part to help clear up public misconceptions about chicken size.

"There's a lot of criticism or ignorance about why chicken grow so fast," said Zuidhof. "If you look at a chicken from 50 years ago and today's chicken, it's natural to say, 'Wow, what's going on, that seems like something that's pretty unnatural.'"

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Researchers compared three types of chickens for the study: one from a breed that hasn’t been selectively bred since the 1950’s, another from a breed that hasn’t been selectively bred since 1978, and a third from the modern, selectively bred Ross 308 broiler breed.

The researchers raised the chickens in the exact same environment using the exact same food. With these controls in place, the modern chicken still grew to over four times the size of the 1950’s breed. Here's what each chicken looked like after 56 days:

That change you see is nothing but the result of 50 years of selective breeding. How can selective breeding lead to such rapid change in chicken populations? It’s simple, lead researcher Dr. Martin Zuidhof says. Chickens produce about 120 chicks per year. These chicks are ready to reproduce themselves after just 25 weeks. Because of how quickly chickens reproduce, it doesn’t take much time at all to selectively breed the biggest chickens from each generation and start seeing bigger, meatier birds.

“The success of the selection parameters is much higher in poultry than it is in other livestock," Zuidhof tells CTV News. "That's why we're not seeing the same kind of gains in cattle and pigs."

Is there any danger in eating these larger chickens? Not at all, Zuidhof says. They’re just a bigger form of the same animal.

"There is no danger in eating larger chickens," Zuidhof told the Huffington Post. "That would be comparable to saying it is more dangerous to eat bigger carrots because they’re bigger."